1. Field of the Invention
The present invention relates to an arrangement for transporting air with the aid of so-called ion-wind or corona-wind, the arrangement being of the kind set forth in the preamble of claim 1.
2. The Prior Art
The arrangement has been developed primarily for use in conjunction with air purifying devices, such as electrostatic precipitators for example, and air processing systems, such as ventilation systems and air-conditioning systems, for example, although the invention can also be used to advantage in many other connections where air is required to be transported, such as when cooling electrical apparatus or electrical equipment, and in conjunction with heating devices, such as electric hot-air blaze.
Today, air is transported in the aforesaid apparatus, systems etc. almost exclusively with the aid of mechanical fans of mutually different design. Such mechanical fans and associated drive motors are relatively expensive, in addition to being heavy and requiring a considerable amount of space. They also have a relatively high energy requirement, and are consequently expensive to run. In operation the fans also generate a considerable amount of noise, which is highly troublesome in many areas in which such fans or blowers are used, for example in dwelling places and in certain working locations.
It is known that the transportation of air can be achieved, in principle, with the aid of so-called ion-wind or corona-wind. An ion-wind is created when a corona electrode and a target electrode are arranged at a distance from one another and each connected to a respective terminal of a direct-current voltage source, the corona-electrode design and the voltage of the direct-current voltage source being such as to cause a corona discharge at the corona electrode. This corona discharge results in ionization of the air, with the ions having the same polarity as the polarity of the corona element, and possibly also electrically charged so-called aerosols, i.e. solid particles or liquid particles present in the air and becoming electrically charged upon collision with the electrically charged air ions. The air ions move rapidly, under the influence of the electric field, from the corona electrode to the target electrode, where they relinquish their electric charge and return to electrically neutral air molecules. During their passage between the electrodes, the air ions are constantly in collision with the electrically neutral air molecules, whereby the electrostatic forces are also transferred to these latter air molecules, which are thus drawn with the air ions in a direction from the corona electrode to the target electrode, thereby causing air to be transported in the form of a so-called ion-wind or corona-wind.
Arrangements for transporting air with the aid of ion-winds are known to the art, and examples of such apparatus are described and illustrated, inter alia, in DE-OS No. 2 854 716, DE-OS No. 2 538 959, GB-A No. 2 112 582, EP-Al No. 29 421 and U.S. Pat. No. 4,380,720. These prior art air-transporting arrangements utilizing ion-wind or corona-wind have been found extremely ineffective however, and have not achieved any practical significance. It would seem that a reason for this is a lack of understanding of the physical mechanisms responsible for the total transportation of air through an arrangement of this kind. Consequently, it is not possible with the previously suggested embodiments of ion-wind operated air transporting arrangements to achieve in practice the transportation of significant quantities of air without needing to raise the corona current to levels which lie considerably above those levels which can be considered acceptable when using such an arrangement in populated environments. It is well known, inter alia, from the electrostatic precipitator field, that an electric corona discharge generates chemical compounds, primarily ozone and oxides of nitrogen, which have an irritating effect on human beings, and which can be harmful to the health when present in the air in excessively high concentrations. In the event of a corona discharge these chemical compounds are generated at a rate which is contingent on the magnitude and polarity of the electric corona current. Consequently, present day electrostatic air filters for use in human, or populated, environments operate with a positive corona discharge and a corona current having an amperage which is substantially proportional to the quantity of air passing through the filter per unit of time in normal operating conditions. In this respect the corona current is of the order of 40-80 .mu.A at an air-throughput of 100 m.sup.3 /h, the strength of the current being adapted to the requirement for an acceptable level of ozone and Nox generation. It will be understood that the corona current utilized in air-transporting arrangements which operate with an ion-wind and are used in the presence of people, i.e. human environments, must also be restricted to the aforesaid magnitude. This is not possible to achieve with the prior art air transporting arrangements utilizing ion-wind, due to the poor efficiency of the arrangements. For example, according to reports, it is possible to achieve with the arrangement proposed in EP-Al No. 29 421 and U.S. Pat. No. 4,380,720 an air throughput of 1 l/s with the aid of a corona power of 1 W at a preferred corona voltage of 15 kV. Thus, when converted to an air throughput of 100 m.sup.3 /h this arrangement will consume about 1900 .mu.A, which is roughly thirty times higher than the corona-current value acceptable in human environments.
Consequently an object of the present invention is to provide an improved and much more effective air transporting arrangement of the kind mentioned in the introduction, and one which is so efficient as to enable it also to be used in practice in a human environment.
The arrangement according to the invention is based on a more profound and improved understanding, previously unachieved, of the mechanisms decisive for the total transportation of air through an arrangement of this kind, and has the characterizing features set forth in the following claims.